Tony Blair will face increased pressure from all parties next week for action to reform Britain's voting system. MPs are hoping to capitalise on a fresh wave of interest in electoral reform when they form a new all-party House of Commons campaign group next week.

Organisers of the Parliamentary All-Party Group on electoral reform, which campaigns for greater understanding of alternative voting systems, believe its 150-strong membership will be swelled because of renewed interest in proportional representation after an election which saw Labour returned on less than 36 per cent of the vote.

Campaigners believe many Labour MPs in newly marginal seats will swing behind reform because their narrow majorities have focused minds on the practical benefits of a change in the electoral system.

One said: "I think some MPs, particularly those in very marginal seats, are keen because they know they have no vested interest in the current system."

Austin Mitchell, Labour MP for Great Grimsby, and vice-chairman of the all-party group in the last Parliament, said the cause of electoral reform had "risen from the dead".

He said: "I think electoral reform has come back from the dead with this election result. Every Labour supporter has to be happy that we are still in government, but unhappy we have a majority in Parliament not based on the level of support we had in the country.

"I think the whole issue will revive in a way it did not during the last Parliament. Most MPs tend to feel that the system that elected them must be good. But nobody outside is happy with a result like this.

"I think support for the group will increase, but I'm looking for more support from the Conservatives."

He added: "The group is mainly about bringing people together to discuss how to further the campaign for reform. Each party has its own electoral reform group, and we are trying to build a consensus."

Richard Burden, Labour MP for Birmingham Northfield and chairman of the all-party group, will highlight the arguments for reform at the Commons on Tuesday in a meeting organised by the Fabian Society. Anne Campbell, former MP for Cambridge and chairman of the pressure group Labour Campaign for Electoral Reform, will also press the case for change.

Mary Southcott, spokes-woman for the group, said support for change was increasing. She said: "Because of the climate created by the general election the campaign has been growing. Because The Independent and other newspapers have been talking about this, the campaign for electoral reform is on the agenda."

The Independent's Campaign for Democracy has gathered pace since it was launched 14 days ago.

More than 33,000 readers have joined the campaign for reform, despite claims by the Lord Chancellor, Lord Falconer of Thoroton, that there was no "groundswell" of support for change.